Myopathies and their Electrodiagnosis2 Randall L. Braddom, M.D., M.S. Clinical Professor Robert Wood Johnson Medical School and the New Jersey Medical School

The Five Steps of EMG  First published by Johnson and Melvin in Johnson EW, Melvin JL. Value of electromyography in lumbar radiculopathy. Arch Phys Med Rehabil (June) :

Remember  STEROIDS QUIET MUSCLE MEMBRANES  EMG PIN CAN CAUSE PROBLEMS WITH MUSCLE BIOPSY

DUCHENNE MUSCULAR DYSTROPHY  Family History, Sex-linked Recessive  Pseudohypertrophy  CK elevation  Reduced or Absent Dystrophin  Gene Deletion  EMG shows fibs, positive waves, myopathic changes early, but hard to find muscle later

DUCHENNE MUSCULAR DYSTROPHY  30 per 100,000 live births  1/3 of cases are new mutations  x-linked recessive  Female carriers with mild weakness and CK elevation due to Lyon hypothesis

CREATINE KINASE IN DMD  Begins in infancy at times normal (usually 10,000 to 30,000)  Declines about 20% per year  CK less than 10 times normal is strong evidence against DMD, except in final stages  Can be in normal range in last stage

GENE ABNORMALITY IN DMD  Located at Xp21 (1977)  DMD gene is large (2000 kilobases) (cloned in 1987) The largest gene  Gene produces Dystrophin (1987)  Southern blot or Polymerase chain reaction (PCR) identifies gene deletions (present in about 60%)  Sporadic cases due to new mutation or germ line mosaicism  Carriers who are negative for gene deletion can be identified by Linkage Analysis

DYSTROPHIN (1987)  Pattern for making it is on Xp21 gene  Only 0.002% of striated muscle protein  Critical to the muscle membrane structure (sarcolemma) (1988)  MDX mouse also has no dystrophin, inherits its disease as x-linked recessive, but has only minor weakness  Dystrophin is also found in smooth muscle, cardiac muscle, neurons and glia  Carriers have reduced dystrophin

BECKER MUSCULAR DYSTROPHY  High CK  Pseudohypertrophy  Sex-Linked Recessive  EMG  Reduced or abnormal dystrophin  Gene deletion

LIMB GIRDLE MD  Autosomal Recessive usually  Onset usually in 20’s-30’s  EMG shows myopathic units, mild muscle membrane irritability  This is a number of diseases we are now genetically separating

FASCIOSCAPULOHUMERAL Muscular Dystrophy  Autosomal Dominant  Pattern of Weakness, especially of face  Can’t whistle, suck through straw  EMG shows myopathic potentials, rare positive wave or fibrillation